Cron Builder with Next-Run Preview
Build a cron expression with dropdowns or by hand, get a plain-English description, and preview the next 10 run times in any timezone.
How to use this tool
- Pick presets in the per-field dropdowns, or type a raw 5-field cron expression — both stay in sync.
- Choose the timezone the schedule should be interpreted in.
- Read the plain-English description and confirm the next 10 run times look right.
- Copy the expression into your crontab / CI config, or share the link to show a teammate.
cron-builder is a two-way cron editor for developers, sysadmins and anyone wiring up a scheduled job. Unlike a plain explainer, it lets you build an expression from per-field dropdowns (minute, hour, day-of-month, month, day-of-week) and edit the raw expression directly — the two views stay in sync. The killer feature is the live next-10-run-times preview rendered in any IANA timezone you pick, so you can verify a schedule actually fires when you expect before you ship it to crontab, GitHub Actions, Kubernetes CronJobs or a cloud scheduler.
Everything runs in your browser. Share a link and the recipient sees the exact same expression and timezone.
Frequently asked questions
- How are the next run times calculated?
- The expression is parsed into the set of allowed minutes, hours, days, months and weekdays, then each upcoming minute is tested in your chosen timezone using the browser's Intl API. This correctly accounts for daylight-saving transitions in that zone.
- Does it follow standard cron day-of-month / day-of-week rules?
- Yes. When BOTH day-of-month and day-of-week are restricted (neither is '*'), Vixie/crontab semantics treat them as an OR — the job runs if either matches. When only one is restricted, it is required. The builder mirrors this.
- Is my schedule sent to a server?
- No. Parsing, the English description and all run-time math happen locally in JavaScript. The only thing in the shareable URL is the expression and the timezone you chose.